Nitrogen fuels brassica crop development and good supplies are required in wrap or guard leaves so that these can provide sufficient assimilates and nutrients for the curd or head. Good leaf/curd ratios and the highest quality compact curds can only be produced by applying optimum high rates of nitrogen.
Correct nitrogen nutrition also improves crop colour and reduces the incidence of brown head in broccoli, which improves marketability.
Potassium boosts plant biomass and resultant brassica head weight and yield.
Supplies of potassium need to be balanced alongside those of nitrogen. Potassium also helps to reduce variability on crop grade at harvest and maintain head and curd compactness.
Sulphur is an important component of enzymes and other proteins, and is required for chlorophyll formation. A steady supply of sulphur throughout the season is needed. Care needs to be taken however, to match sulphur and nitrogen supply. Increasing nitrogen supply can restrict sulphur uptake. This is either a dilution effect due to better growth or a direct competition for uptake.
Iron is the micronutrient needed in greatest quantities within brassicas – between 80- 90g/t Fe – and over four times as much iron is needed compared to boron or zinc. It is important to plant metabolism as a component of enzymes and proteins, in order to increase brassica size and weight.